This invention is directed to an electronic timepiece having frequency rate adjustment circuitry, and in particular, to an electronic timepiece having timing rate adjustment circuitry for comparing the timing rate to a randomly selected reference period in order to automatically regulate the timing rate thereof.
In general, electronic timepieces are formed of three components, two of which are primarily responsible for the accuracy thereof. A first component is an oscillator circuit having a high frequency vibrator as a time standard for producing a high frequency signal, which signal is applied to a divider circuit. The divider circuit is a second component and divides down the high frequency signal to produce a low frequency timekeeping signal, which timekeeping signal is applied to the third component, which component is a conventional analog or digital display. As noted above, the accuracy of the time displayed is dependent upon the accuracy of the high frequency signal produced by the oscillator circuit and the ability to vary the division ratio of the divider circuit and hence adjust the timing rate of the low frequency timekeeping signal produced thereby.
In the art, three approaches have been utilized to adjust the timing rate of the electronic timepiece circuitry. A first approach is to vary the impedances in the oscillator circuit, and in particular, to vary a tuning capacitor, in order to vary the high frequency signal produced by the oscillator circuit, often referred to as the primary frequency. A second approach is to adjust the division ratio of the divider circuit and thereby change the timing rate of the low frequency timekeeping signal produced thereby without effecting any change in the operation of the oscillator circuit. A third approach combines both the first and second approaches by varying both the primary frequency produced by the oscillator circuit and by varying the division ratio of the divider.
Although each of the approaches noted above is effective in improving the accuracy of the low frequency timekeeping signal, changes in the environment, such as temperature changes, aging of the quartz crystal vibrator utilized as time standards for the oscillator circuits, and changes in the effective supply voltage, result in additional variations in the primary frequency which are unaccounted for during manufacture and sale of the electronic timepiece. Accordingly, electronic timepiece circuitry for adjusting the timing rate during operation to take into account changes in the primary frequency is desired.